Application of Organometallic
Chemistry – Breaking the Inert
C-H Bond
Literature Special Topic
Date
Created by [John Lee, University of Tennessee Chattanooga, John-Lee@utc.edu] and posted on VIPEr
(www.ionicviper.org) on [July 16, 2012], Copyright [July, 16, 2012]. This work is licensed under the Creative
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You want to break which bond!
Example Organic Molecules
-Why do we draw line structures for
Organic molecules?
-High bond energy
methane 100 kcal/mol
benzene 110 kcal/mol
-High pKa
on the order of >40
**,but…Nature uses the C-H bond: See methane monooxygenase and vitamin-b12
In organic chemistry….
Generic Substitution Reaction (SN1 shown)
Leaving Groups (LG)
TsO-, NH3 > I-, H2O > Br- > Cl- > HO-, NH2-, RO-
Carey, F. A. Organic Chemistry, 4th ed. 2001, McGraw-Hill,
Chapter 8.
In organometallic chemistry….
Cross-Coupling Reactions
Heck, R. F.; Negishi, E.; Suzuki, A. palladium catalyzed cross couplings in Organic Synthesis: Great Art in a Test Tube.
http://nobelprize.orglnobeljrizes/chemistry/laureatesl}O10/press.html (March 17, 2011).
but wait I said C-H not C-X activation?
If it ain’t broke why fix it?
-Nearly everything comes from coal, oil or natural gas
Coal: 1,000 – 2,000 years
Oil: 50 – 150 years
Natural gas: 207 – 590 years
-However this is not sustainable for population growth
Why?
-We are a good 10-20 (optimistic) years from solar
-For the interim time we should use our resources to the
best of our ability
How?
Lewis, N. S.; Nocera, D. G. Proc. Nat. Acad. Sci. 2006, 103,
15729-15735.
How? Rationale design and synthesis
Metal
+
Ligands
C-donor,
N-donor,
O-donor,
P-donor,
or S-donor etc…
What it is really all about!
Shriver and Atkins Inorganic Chemistry, 5th ed. 2001, Freeman, Chapter 1.
Some typical mechanisms
Labinger, J. A.; Bercaw, J. E. Nature 2002, 417, 507-514.
Example 1: Oxidative addition
Qualitative MO Diagram
-The metal’s oxidation state increases by two units
Must be accessible
-Requires an electron rich metal
Low oxidation state
Electron donating ligands
-The metal’s coordination # increases by two
Must be accessible
-Many d8 metals meet these criteria:
Primarily RhI and IrI
Sometimes PdII and PtII
Example of oxidative addition:
Alkane dehydrogenation
Example 2: s-Bond metathesis
Qualitative MO Diagram
-Early transition metals that do not have a n+2
oxidation state available
-Late transition metals that do not have an
accessible n+2 oxidation state
-Many d0 metals meet these criteria:
For example, ScIII, ZrIV, TaV
Example of s-bond metathesis:
Hydromethylation of propylene
Sadow, A. D.; Tilley, T. D. J. Am. Chem. Soc. 2003, 125, 7971-7977.
Example #3: Electrophilic substitution
Qualitative MO Diagram
Milstein, D. et al. J. Am. Chem. Soc. 1998, 120, 12539-12544
Example of electrophilic substitution:
Methane oxidation
Periana, R. A.; Taube, D. J.; Gamble, S.; Taube, H.; Satoh, T; Fuji, H.
Science 1998, 280, 560-564.
C-H Functionalization: A challenge
C-C Bond Formation – Olefin Insertion
Foley, N. A.; Lee, J. P.; Ke, Z.; Gunnoe, T. B.;
Cundari, T.. R. Acc Chem. Res. 2009, 42, 585-597.